1. Field of the Invention
The present invention relates to a tungsten chemical vapor deposition method and a method for forming a tungsten plug, and more specifically, to a tungsten chemical vapor deposition method and a method for forming a tungsten plug capable of preventing a fluoride ion generated during a tungsten deposition process from reacting with the barrier layer at an edge portion.
2. Description of the Related Art
An aspect ratio of a contact hole or a via hole, i.e., the ratio of the length of a hole to its diameter, is increased as the size of the device in which it is formed is miniaturized by high integration of the device. Since contact holes or via holes cannot be formed reliably using the conventional aluminum deposition technology, a tungsten plug is commonly formed in a contact hole or in a via hole using tungsten chemical vapor deposition (CVD).
In general, a tungsten plug is formed by first forming a first conductive layer on a wafer and then covering the surface with a flat insulation layer. After forming a contact hole or a via hole on the insulation layer, a Ti/TiN barrier layer is blanket deposited on the wafer. Then, tungsten is deposited on the barrier layer to a sufficient thickness such that the contact hole or the via hole can be sufficiently buried by tungsten CVD. A tungsten plug is formed in the contact hole or in the via hole by polishing the surface of the deposited tungsten layer to make the layer flat using an etchback process or chemical mechanical polishing method until the surface of the insulation layer is exposed.
When using the tungsten CVD process to form the tungsten plug, there occurs a volcano phenomenon as set forth in U.S. Pat. No. 5,489,552, incorporated herein in its entirety by reference. That is, in a tungsten CVD, tungsten is deposited on the surface of the Ti/TiN barrier layer by reducing a tungsten fluoride gas with a silane gas or a hydrogen gas. At this time, TiFx vapors are generated by such that a fluoride ion generated by the reduction reaction reacts with Ti of the bottom layer through a pin hole on the TiN layer forming the barrier layer, and as the volume of the Ti layer increases by the reaction, the Ti layer penetrates the top layer, and a defect occurs similar in shape to a volcano eruption.
To solve said problem, U.S. Pat. No. 5,489,552 discloses a technology preventing the volcano phenomenon by blocking the fluoride ion generated in the succeeding reaction process from reacting with the bottom film by annealing the surface of the barrier layer or by applying a passivation to the surface of the TiN layer with a silane gas at a flow rate ranging from 75 to 300 SCCM for from 25 to 150 seconds at the CVD initial step.
On the other hand, the tungsten deposited by the tungsten CVD method is removed by an etchback method or by the CMP method. The removal of the tungsten formed on the edge part of the wafer is readily accomplished using the etchback method, but in the CMP method it is difficult to remove the tungsten deposited on the edge part, that is, on the side or on the back surface because only the top surface of the wafer is polished. The residue on the edge part is dropped in the succeeding process and contaminates the facility or acts as a contaminant.
In Japanese Pat. Publication No. 8-213344 is disclosed a ring clamp covering the edge part in order to prevent a reaction gas from contacting directly in order to prevent in advance the creation of a tungsten residue remaining on the edge part of the wafer when forming a tungsten plug. The Japanese publication also discloses a technology of supplying a fluoride gas capturing gas like an ethylene CH2 toward the edge part of the wafer from the bottom of the edge part.
In U.S. Pat. No. 5,953,630, incorporated herein in its entirety, is disclosed a technology of forming a passivation film on the edge part by supplying a purge gas including halides such as NF.sub.3, C.sub.2F.sub.6, Cl.sub.2, F.sub.2, ClF.sub.3 and BCl.sub.3 toward the edge part of the wafer from the bottom of the edge part of the wafer.
If the deposition of tungsten on the edge part of the wafer in a tungsten CVD process is not prevented actively, the barrier layer is lifted by the volcano phenomenon generated on the edge part, and the reaction continues to proceed toward the center of the wafer along the lifted interface and results in generating a device defect and in reducing the yield.
It is an object of the present invention to provide a tungsten chemical vapor deposition method and a method for forming a tungsten plug which can prevent a fluoride ion generated during a tungsten deposition process from reacting with the barrier layer at the edge part by applying a passivation not only to the top surface of the wafer but also to the edge part with silane gas at the initial step of the tungsten deposition process.
To accomplish the above object, a chemical vapor deposition method of the present invention includes forming a tungsten layer on a wafer having a top surface and a peripheral edge portion. A silane gas is supplied to each of the top surface and the edge portion of the wafer before the deposition of tungsten, in order to form a silicon passivation thin film on the top surface and on the edge portion of the wafer to prevent a fluoride ion generated in reaction from penetrating into a bottom layer through a pin hole.
In another aspect, the deposition method of the present invention includes preparing a wafer where a barrier layer is formed. Silane gas is supplied from a top of the wafer and from a bottom of an edge portion toward the wafer simultaneously, in order to form a silicon passivation thin film on the top surface and the edge portion of the wafer. In order to form a tungsten nucleation on the top surface of the wafer where the passivation thin film is formed, a mixed gas including a tungsten fluoride gas and a silane gas is supplied from the top of the wafer toward the wafer, and at the same time silane gas is supplied from the bottom of the edge portion toward the wafer. A mixed gas including a tungsten fluoride gas and a hydrogen gas is supplied from the top of the wafer toward the wafer, in order to deposit a sufficiently thick tungsten on the surface of the wafer.
In another aspect, the invention is directed to a method for forming a tungsten plug in a semiconductor device. A hole is formed on an insulation layer on a wafer, and a titanium thin film is deposited with a uniform thickness on the resulted structure. A titanium nitride film is deposited with a uniform thickness on the titanium thin film. A silicon passivation thin film is formed on the titanium nitride film by supplying silane gas to each of a top surface and an edge portion of a wafer deposited with the titanium nitride film. A tungsten nucleation is formed on the top surface of the wafer as supplying silane gas to each of the top surface and the edge portion of the wafer where the silicon passivation thin film is formed. Tungsten is deposited on the top surface of the wafer where the tungsten nucleation is formed, in order for the hole to be filled sufficiently.
In one embodiment, it is desirable to form the silicon passivation thin film with a thickness of at least about 10 angstroms by supplying the silane gas supplied to form the silicon passivation thin film at a flow rate ranging from 30 to 50 SCCM for about 5 or 30 seconds in a vacuum chamber maintaining the temperature of about 415 degrees C. and the pressure of about 40 Torr. That is, it is sufficient to be as thick as to fill in a pin hole of the barrier layer.
In one embodiment, the final thickness of the deposited tungsten is about 4,000 angstroms.
In one embodiment, the wafer is clamped with a ring clamp for preventing a tungsten fluoride gas from contacting directly with the edge part of the wafer.
The present invention can prevent a fluoride gas generated in a tungsten deposition process of a succeeding process from penetrating into a titanium thin film through a titanium nitride film on the edge part of the wafer by applying passivation to not only the top surface but also to the edge part of the wafer, in an initial step of the tungsten deposition process. Therefore, the present invention can improve the yield and the reliability since the volcano phenomenon, which occurs on the edge part and proceeds toward the center of the wafer, can be prevented as the reaction of the titanium and the fluoride gas is stopped.